In recent years, in air conditioning apparatus equipped with devices such as compressor and fan, a 3-phase brushless DC motor, for example, has been used as the power source of these devices.
Generally, a 3-phase brushless DC motor has a rotor (hereinafter called a rotor), which comprises a permanent magnet having plural magnetic poles, and a stator (hereinafter called a stator), which has 3-phase drive coils. Drive voltages corresponding to the position of the rotor with respect to the stator are applied to the drive coils of this brushless DC motor by a motor drive control device for driving and controlling this motor. Thus, currents corresponding to the drive voltages flow in the drive coils, a magnetic field is generated, and the rotor rotates.
Here, among methods of detecting the position of the rotor with respect to the stator, a method using three rotor position detection sensors placed so as to correspond to each of the 3-phase drive coils is often used. These rotor position detection sensors are for detecting the relative position of the rotor with respect to the stator on the basis of the magnetic field that has arisen because of the permanent magnet of the rotor, and specific examples thereof include Hall elements and Hall ICs. However, when trouble such as a fault arises in these position detection sensors, the position detection sensor in which the trouble has arisen becomes unable to normally detect the position of the rotor. In this case, the motor drive control device ends up applying to the motor drive voltages where, for example, the half cycle of one cycle has a normal waveform but the remaining half cycle has a waveform that is out of phase. When this happens, there is the fear that the currents energizing the motor will increase, that motor noise and vibration will increase, and that the rotation of the motor will become unstable.
Thus, for example, as described in patent document 1 (JP-A No. 8-331886) and patent document 2 (JP-A No. 2000-184774), there are known motor drive control devices that detect whether or not trouble is arising in the position detection sensors. The motor drive control devices of patent document 1 and patent document 2 stop driving the motor when they have detected that there is trouble in the position detection sensors.